Deficiencies Of Previous Models Research Articles

Experimental study and modeling permeability damage in porous media due to asphaltene deposition

Asphaltene deposition in porous media has a destructive effect on well productivity during primary and secondary oil recovery. Previous research studies have presented models for permeability reduction due to particle deposition in porous media. In this study, a semi-experimental model was modified and a new model was introduced to predict permeability changes due to asphaltene retention in early times of precipitation. The modified model unlike common models considers the size of asphaltene particles, porous media grain size, fluid flow properties and precipitation in pore throat. A set of experiments are done to obtain the parameters needed for modeling and check the validity of model. Crude oil is used as fluid sample and a sand pack filled with glass beads is used as an artificial porous media in flood tests. To identify the size of asphaltene particles, microscopic technique is used. The results of experiments are used to investigate asphaltene deposition in porous media and evaluate model prediction. A new procedure based on the modified model is applied to obtain model parameters and simplify the calculations. The new model can eliminate the deficiencies in previous models for prediction of asphaltene deposition in early stages of particle retention. The model also is validated by experimental results that were reported in the literature before. The results show rational accommodation with experimental data.

Enhanced tools for predicting annual stone pine (Pinus pinea L.) cone production at tree and forest scale in Inner Spain

Aim of the study: To present a new spatiotemporal model for Pinus pinea L. annual cone production with validity for Spanish Northen Plateau and Central Range regions. The new model aims to deal with detected deficiencies in previous models: temporal shortage, overestimation of cone production on recent years, incompatibility with data from National Forest Inventory, difficulty for upscaling and ignorance of the inhibitory process due to resource depletion.Area of study: Spanish Northern Plateau and Central Range regions, covering an area where stone pine occupies more than 90,000 haMaterial and methods: Fitting data set include 190 plots and more than 1000 trees were cone production has been annually collected from 1996 to 2014. Models were fitted independently for each region, by means of zero-inflated log normal techniques. Validation of the models was carried out over the annual series of cone production at forest scale.Results: The spatial and temporal factors influencing cone production are similar in both regions, thus the main regional differences in cone yield are related with differences in the phenological timing, the intensity of the influent factors and forest intrinsic conditions. A significant inhibition of floral induction by resource depletion was detected and included into the model. Upscaling the model results in accurate prediction at forest scale. Research highlights: [1] The new model for annual cone production surpass the detected deficiencies of previous models, accurately predicting recent decay in cone production; [2] Regional differences in cone production are due to phenological and seasonal climatic differences rather than to between provenances genetic differencesKeywords: zero-inflated models; pine nut; conelet losses; Leptoglossus occidentalis; forest upscaling.

A computational model of pulmonary gas transport incorporating effective diffusion

A computational model of gas transport in the lung is described which remedies many of the deficiencies of previous models, as listed by Chang and Farhi (1973), in that it allows for fluctuating lung dimensions, gas exchange, simultaneous convection and diffusion, and the enhanced effective diffusion that occurs when convective flow is also present. The results of calculations using the model are presented, showing the maximum effect of Taylor diffusion. The actual magnitude of Taylor diffusion, suitably modified to allow for the disturbed conditions within the lung, is considered in the light of recent experiments.